1. Technical Field
The present invention generally relates to landing gear for a trailer. More specifically, the invention relates to landing gear which is vertically adjustable by hydraulic power. Specifically, the invention relates to vertically adjustable landing gear driven by a dual output hydraulic motor which directly operates the transverse drive shaft which engages a mechanical lift mechanism in the lifts.
2. Background Information
Landing gear for trailers such as used with tractor trailers and the like have been known for many years. Various mechanisms have been utilized to raise and lower the landing gear, including jack screw or other threaded mechanisms, pneumatically powered mechanisms and hydraulically powered mechanisms which pump hydraulic fluid into telescoping piston-cylinder type legs to provide the lift mechanism. Most commonly, these landing gear are cranked by hand to make the vertical adjustment. U.S. Pat. No. 3,201,087 to Dalton discloses a landing gear having telescoping legs which are driven by a threaded member with the use of beveled gears translating motion from a transverse drive shaft. This patent shows both the use of a hand crank and motor power in order to make the vertical adjustment. U.S. Pat. No. 4,466,637 to Nelson also discloses a landing gear which is either operated manually or by a motor, in particular by an air motor. While it is assumed that each of these devices operates as described, each of them also requires a reduction gear box in order to function properly. By contrast, the present invention does not require such a reduction gear box, but instead directly drives the transverse shaft which engages the vertical lifts of the landing gear via beveled gears (such as disclosed in the Dalton patent) or otherwise in order to vertically adjust the lift.
U.S. Pat. No. 3,784,160 to Phillips discloses a system for raising and lower landing gear which uses an electric motor having an output shaft and a casing rotatable in opposite directions with respect to one another, the shaft and casing also being rotatable with respect to the vehicle with which they are used. The output shaft is connected to one drive shaft and the casing to another drive shaft so that the drive shafts rotate in opposite directions in accordance with the output shaft and casing to operate respective screw jacks. There are several disadvantages of this arrangement, wherein a motor is not mounted to the vehicle so that the casing is rotatable with respect to the vehicle. A “free-floating” motor precludes the use of hydraulic and other motors which must be stationary in order to receive the pressure/return lines. Thus, only a motor which can achieve this “free-floating” nature may be used. An electrical motor may be the only type which can function in this manner. The electric motor thus requires a brush assembly to simultaneously provide power and allow the casing to rotate. In addition, in order to provide the necessary torque to lift heavy loads, the motor would need to be of a substantial size and weight, inherently adding lateral stress to the drive shafts extending to the jacks and to the motor bearings supporting the output shafts, thus requiring drive shaft supports to indirectly support the weight of the motor and maintain alignment of the drives shafts and output shafts.
U.S. Pat. No. 4,345,779 to Busby discloses a pneumatically operated drive unit which drives a shaft via a nut attached to the end of the shaft, the pneumatic drive and nut being disposed laterally outside a pair of telescoping legs. One disadvantage of this arrangement is that the drive provides a pulsating drive which does not promote smooth operation which is highly desirable for vertically adjusting the landing gear. Another drawback of this system is the limit on the amount of pressurized air that can be maintained at sufficient pressure in mobile air reservoirs. In order to have sufficient air, the air reservoirs must be sufficiently large, which means a bulky reservoir that is impractical to carry on the vehicle. Where the reservoir is too small to completely adjust the landing gear, an air compressor must be used to provide the additional pressurized air needed to provide powered adjustment, again adding to the bulk. As is known in the art, it can take a substantial amount of time for an air compressor to build up sufficient pressure for a given purpose. Adjusting the landing gear in a reasonably short time is one of the desired outcomes of a powered lift, and thus this is another drawback of such a pneumatic unit. In addition, positioning the drive unit outside the telescoping legs exposes the unit to damage during transport.